1. Field of the Invention
This invention relates to the production of flaked metal powders.
It is understood that the expression "flaked metal powders" means metal or alloy platelets whose ratio of thickness to length is smaller than 0.1. On the other hand, as used in the present specification and in the appendant claims the term "metal powder" should be understood to mean "flaked metal powder", unless otherwise stated.
2. Description of the Prior Art
The conventional way of producing such powders is by the use of a tube ball mill in which starting metal particles are tumbled together with grinding elements to produce a high ratio of impact to attritive action. This method has certain limitations and can be generally said to be relatively inefficient and time consuming.
Tundermann's U.S. Pat. No. 3,709,439, issued Jan. 9, 1973 discloses a process for producing metal flakes from metal powder made of a stain-resisting metal or alloy thereof in which a charge of the powder is milled in a mobile liquid medium in the presence of grinding bodies confined in a milling space. The volume ratio of the liquid medium to the metal powder is at least 10:1 to 50:1. Subsequently all the interstitial space between the grinding bodies when at rest in the milling space is filled with the liquid medium. The liquid medium contains a small amount of lubricant effective to coat the flaked product. The starting metal powder has a particle size preferably passing about 100 mesh and preferably the milling is continued until the thickness of at least a substantial portion of the metal powder is reduced below about 1 micron. The volume ratio of the liquid medium to the metal powder is given as at least 20:1.